Why do new cars suddenly have lower MPG ratings?

Dear Car Talk

Dear Car Talk | Aug 01, 2008

Dear Tom and Ray:

I have noticed that most, if not all, new cars have lower miles-per-gallon estimates for 2008 than they had for 2007. Why is this? Are the cars less efficient, or are the ratings stricter? -- Ray

TOM: The EPA fuel-economy numbers were, in fact, adjusted downward in 2008 in an attempt to get them from "ridiculous" to "plausible."

RAY: Before 2008, everybody knew that the EPA numbers were not real -- meaning that nobody would ever get the mileage that the EPA claimed the car would get. If the EPA said a car got 20 miles per gallon around town, you'd be lucky to get 15. In fact, the real-world, city numbers were probably 30 percent lower, on average, than the EPA estimates.

TOM: So, the only real use for the EPA numbers was for comparison purposes. In other words, if you were buying a 2000 Ford Expedition, you knew it would never really get the 12 miles per gallon around town that the EPA estimated, but you knew that the same year's Honda CR-V -- EPA-rated at 22 mpg city -- was almost twice as good. And that was well worth knowing.

RAY: But it was time for an update. The original tests were done in the 1970s. And besides being done under "ideal" conditions, they didn't reflect how people drive now. So the EPA made some changes.

TOM: People drive at higher speeds now than they did during the "Speed Limit 55 MPH" days of the '70s. And higher-speed driving uses a lot more fuel. So the EPA added a high-speed component to its tests.

RAY: Almost all cars have air conditioning now, which was not true in the '70s. AC use increases fuel consumption. So portions of the new test are done with the air conditioner on.

TOM: The old tests were done at ideal temperatures, which don't reflect the reality of drivers in cold-weather states, where cars are warmed up for minutes on end in the morning, and burn fuel less efficiently when they're cold. So, the new tests include a cold-weather component.

RAY: And finally, rather than driving like Nedley the Nerd during the tests and accelerating as if there were a police officer with a grudge on your tail, the new tests add some hard acceleration phases, to reflect getting onto highways and passing other vehicles.

TOM: I notice they don't have an "arm out the window, holding lit cigar, with mother-in-law in back seat" test yet, do they?

RAY: Not yet. Anyway, the new tests, of course, are still valid for comparison shopping, but they're also much closer to the fuel economy you'll actually get with these vehicles. In fact, Consumer Reports says that in a few cases, they even got better mileage than the new EPA estimates.

TOM: So, while the numbers are lower, they're at least real numbers now. If you'd like to see more information on the EPA mileage ratings and a list of every car sold in America and its EPA fuel-economy numbers, check out www.fueleconomy.gov.

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